1. Field of the Invention
This invention relates to a porous matrix. More particularly, the present invention relates to porous matrices which are intended to be used in the animal body and which are formed in situ at a target tissue site.
2. Related Art
Many patent applications describe the use of gels or sols, especially hydrogels, for use as tissue scaffolds. For example, WO 00/23054 describes the use of polyvinyl alcohol microspheres in the occlusion of blood vessels or embolizations. WO 99/15211 and WO 00/64977 describe the use of hydrogels as a tissue scaffold. The hydrogels are implanted into a patient in order to support tissue growth and or repair.
The use of hydrogels as tissue scaffolding is problematical in that although the gels themselves may adequately fill the cavity into which they are inserted, they have poor diffusion properties and as such drugs, nutrients or other factors to be supplied to the tissue do not adequately diffuse through the gel. This problem is exacerbated where the gel is seeded with living cells since the poor diffusion of nutrients can lead to premature cell death, possibly resulting in failure of the treatment. A further problem associated with gel scaffolds is that the cross-linking methods used to stabilize or solidify the gels, especially in situ, can damage the entrapped cells.
Scaffolds based on water-insoluble polymers are also known in the art, for example WO 99/25391 describes the use of poly (lactide-co-glycolide) (PLGA) as a polymer scaffold for the regeneration of tissue, especially bone tissue. The polymers are processed so as to form a porous structure. As with the hydrogels, the water-insoluble polymers are implanted into a patient in order to support tissue growth and or repair.
However, the disadvantage of such water-insoluble polymers is that they can only fill cavities with an open shape and methods of shaping the materials are yet to be perfected. Additionally, where the scaffold is to be seeded with cells, the seeding is inefficient (few pores are filled with cells) or the cells are damaged by the structure during the seeding process, and the surrounding tissue cells may also be damaged by the implantation procedures.
WO 99/11196 describes the use of a particulate matrix as tissue scaffold, the particles having internal cross-linking to stabilize the structure of the particle.
Similarly, PCT/GB02/02813 describes an open porous matrix of particulate material for in vivo use in or on a target tissue in medicine, the matrix comprising particles cross-linked with one another so as to define pores therebetween.